1. Field of the Invention
The present invention relates to a memory unit that is capable of indicating the status of the memory.
2. Description of the Related Art
Recently, a non-volatile semiconductor memory known as “flash” memory has been developed and has been used in many fields.
The number of times that information, such as data and programs can be written and deleted (the number of write operations) in flash memory is limited and therefore, flash memory has a limited service life with respect to write operations. For example, some flash memories are capable of only 300,000 to 1,000,000 write operations. As the number of actual write operations approaches the upper limit, it becomes impossible to accurately write information (i.e., writing errors will occur), or the stored information may degrade (i.e., memory errors will occur). Therefore, if the useful life of a flash memory is approaching the end of reliable usage, the user will preferably transfer any data stored in the flash memory to a new memory, so that important data is not lost or damaged.
Presently, no proposals have been suggested to accurately notify an operator that the flash memory is approaching the end of its useful life. Instead, calculations of useful life have been based upon estimates of the number of write operations that have been performed in the given environment.
However, if the actual number of write operations is in fact larger than the estimated number, the flash memory may reach the end of its useful life much earlier than the operator anticipated. In this case, the operator may lose important data if the memory is not timely replaced. On the other hand, if the actual number of write operation is instead less than the estimated number, the semiconductor memory may be prematurely replaced.